Construction of an opposed-piston engine cylinder assembly is well understood. The cylinder assembly includes a liner (sometimes called a “sleeve”) retained in a cylinder tunnel formed in a cylinder block. The liner includes a bore and longitudinally displaced intake and exhaust ports, machined or formed in the liner near respective ends thereof. Each of the intake and exhaust ports includes one or more circumferential arrays of openings in which adjacent openings are separated by a solid portion of the cylinder wall (also called a “bridge”). An intermediate portion of the liner exists between the intake and exhaust ports. In an opposed-piston engine, two opposed, counter-moving pistons are disposed in the bore of a liner with their end surfaces facing each other. At the beginning of a power stroke, the opposed pistons reach respective top dead center (TDC) locations in the intermediate portion of the liner where they are in closest mutual proximity to one another in the cylinder. During a power stroke, the pistons move away from each other until they approach respective bottom dead center (BDC) locations in the end portions of the liner at which they are furthest apart from each other. In a compression stroke, the pistons reverse direction and move from BDC toward TDC.
The intermediate portion of the cylinder lying between the intake and exhaust ports bounds a combustion chamber defined between the end surfaces of the pistons when the pistons are near their TDC locations. This intermediate portion bears the highest levels of combustion temperature and pressure that occur during engine operation. The presence of openings for engine components such as fuel injectors, valves, and/or sensors in the intermediate portion diminishes the cylinder assembly's strength and makes the cylinder liner vulnerable to cracking, particularly through the fuel injector and valve openings.
Heat loss through the cylinder liner is a factor that degrades engine performance throughout the operating cycle of an opposed-piston engine. Combustion occurs as fuel is injected into air compressed between the piston end surfaces when the pistons are in close mutual proximity, forming the combustion chamber. Loss of the heat of combustion through the liner reduces the amount of energy available to drive the pistons apart in the power stroke. By limiting this heat loss, fuel efficiency would be improved, heat rejection to coolant would be reduced, and higher exhaust temperatures can be realized. Smaller cooling systems and lower pumping losses are just some of the benefits of limiting heat loss through the cylinder assembly. It is therefore desirable to retain as much of the heat of combustion as possible within the cylinder assembly.
An opposed-piston cylinder assembly construction according to the present disclosure satisfies the objective of heat containment, thereby allowing opposed-piston engines to operate higher heat retention than opposed-piston engines of the prior art.